How to open a .glb or .gltf file in blender?
Blender comes with glTF-Blender-IO pre-installed since 2.80.

This is a refactoring of the original Khronos glTF exporter, combined with @Julien's importer.  Both of the original projects should be considered obsolete in favor of the newer, combined glTF-Blender-IO project.

The Blender Manual includes documentation on ways to use glTF.